New prostate cancer study clouds PSA debate

NEW YORK (Reuters Health) - A new study suggests men with advanced prostate cancer may live longer in the "PSA era" than they did before the screening test began to gain a foothold in the early 1990s.

The findings - which a leading cancer expert said were problematic - stoke the heated debate over prostate cancer screening using the prostate-specific antigen (PSA) test. Many researchers now fear routine testing may lead to aggressive treatments that do more harm than good.

For the new study, published in the Journal of Urology, researchers tapped into data from three clinical trials involving more than 3,000 men who got hormone treatment for prostate cancer that had spread to the bones and other body parts.

The average patient survived 30 months after starting treatment in 1985 to 1987. By 1989 to 1994, survival was three months longer and by 1995 to 2009, well into the "PSA era," it had reached 49 months.

"It's a remarkable difference," said Dr. Ian Thompson, who heads the Cancer Therapy and Research Center at the University of Texas Health Science Center at San Antonio and led the study.

"The translation of this is, might it very well be that for advanced prostate cancer finding it earlier may allow the earlier initiation of therapy that may then reduce the death rates from the disease?" he told Reuters Health.

But the chief medical officer of the American Cancer Society, who was not involved in the work, said the study has a number of serious shortcomings.

For instance, other trials done by the same research group but involving non-Hodgkin lymphoma, a group of blood cancers, also show patients live longer over time, according to Dr. Otis Brawley.

And that's despite the facts that doctors don't screen for the disease and that patients got the same treatment for their disease.

"There is a cohort effect that we have seen numerous times in medicine," said Brawley, who has collaborated with Thompson on earlier research.

He added that the reasons for the improved survival over time are unclear, but could be related to advances in medical care and infection control.

It is also possible that men today are more aware of symptoms that would have been ignored a quarter-century ago, such as trouble urinating, Brawley said.

"Awareness of the disease increases the chances that you are going to be diagnosed with it and that you will do better," said Brawley.

That, along with better healthcare, may also help explain why the survival gap between black and white men narrowed over time in the new study, he added.

DIFFERENCE DIFFICULT TO EXPLAIN

Finding a tumor due to symptoms is different from finding it through screening, which per definition is done in symptom-free people.

When people have symptoms, their disease is typically more serious, and so people diagnosed with cancer as a result of screening automatically live longer with their disease than those diagnosed based on symptoms - whether or not they get treatment.

This phenomenon, known as lead-time bias, is another limitation of the new study, which Thompson acknowledged.

He said that even after accounting for factors that are tied to earlier death in prostate cancer - such as extensive disease, bone pain and high Gleason scores (a grading system) - men in the later trial still survived longer.

"You cannot say that PSA testing is the cause for this improvement, but when you eliminate all the other potential explanations there is something else there that is playing a role," he said.

But eliminating those other differences through statistics - in other words, trying to cancel out the differences in cancer risk and stage among the men - would also wash out any potential effect of screening. That's because the point of screening is to catch the cancer as early as possible.

Acknowledging that, Thompson said, "I guess I have a difficult time explaining the difference" in survival.